Mobility reduction and apparent activation energies produced by hopping transport in the presence of Coulombic defects

Abstract

A Monte Carlo simulation is proposed to study the mobility reduction due to coulombic defects for hopping transport in a one-dimensional regular lattice. Hops between energetically equivalent sites and within an exponential distribution of energy levels are considered. In absence of coulombic wells, the calculations reproduce the wellknown features of gaussian and highly dispersive transport respectively. When the field due to coulombic potential wells is superimposed to the applied one, the macroscopic conduction features change dramatically. The computed apparent mobilities or transittimes exhibit a Poole-Frenkel character and a modified Arrhenius temperature dependence. Their activation energy differs from the mean energy characterizing hops at the microscopic scale and it is found to depend on parameters such as the defect charge.

Charge Transport in Imperfect Organic Field Effect Transistors: Effects of Explicit Defects and Electrostatics

“…As mentioned above, charge transport through organic semiconducting materials is understood to occur via forms of hopping transport, based fundamentally on a bimolecular charge transfer step. As mentioned above, charge transfer rates can be computed using Miller-Abrahams theory , or Marcus−Hush theory, which is more reliable for organic electronic materials, where Δ G 0 , H ab , and λ are the difference in energy between molecular sites, the electronic coupling matrix element between the orbitals involved, and the total reorganization energy of the reaction. H ab has been shown to be dependent on the intermolecular distance, making eq 1 an example of variable range hopping. , The reorganization term describes the classical density of states, and the exponential term describes the population of molecules that possess the energy required to traverse the electron transfer barrier .…”

“…Very few studies of FET devices include the effects of Coulomb interactions between the charge carriers or between carriers and charged defects . This is not possible to study experimentally and is often excluded from theoretical studies, since including these interactions is computationally taxing, although some previous work has addressed Coulomb effects in other types of transport .…”

Silica-based scintillators: basic properties of radioluminescence kinetics

“…As far as carrier thermalize in extended states above the band edges, thermal velocities vary with temperature T in T 1/2 . In silica, holes are however subject to dispersive transport due to multiple trapping and hopping within localized states at the top of the VB which is strongly affected by disorder [32,33]. Such motions have more complicated variations with T as, probably, cross-sections.…”

“…The density of electron traps is simply that of dopants. For typical doping levels, say 0.1 wt% [23], N is about a few 10 18 cm −3 and is probably lower than H. Indeed, holes are subject to strong localization right above their mobility edge because of disorder-induced localized states [32,33] and of the formation of STHs [27,35]. Therefore, the density of hole traps H introduced in the model is not solely associated with the presence of defects.…”

Electric dipole moments and disalignment of interstellar dust grains

“…Electrons and holes can hop from site to site with assistance from a phonon (e.g., Mott & Davis 1971;Blaise 2001), so no grain is perfectly insulating. The rate at which an electron hops from site i to site j is typically approximated as (Ambegaokar et al 1971;Mady et al 2007), where ν ph ∼ 10 13 s −1 is the phonon frequency (Brucato et al 2002), rij is the distance between sites i and j, d ψ is the electron localization length, Wi→j = max[Ej − Ei, 0], Ei is the electron energy when localized at site i, and T d is the dust temperature.…”